Wireless communication portable terminals such as mobile phones are becoming significantly more sophisticated, smaller, and lighter. Also, with increasing demands for high-speed and high-volume communication, high-frequency communication in which signals are sent and received by using microwave or millimeter wave is rapidly spreading. From this perspective, a compact, light-weight, and thin-profile high-frequency circuit that is compatible with microwave or millimeter wave is sought after.
On the other hand, with a recent trend toward a larger screen size, a display section of a wireless communication portable terminal often has a relatively large area. Therefore, if it is possible to mount a device in the display section, the mounting area of the device can be expanded. When mounting a device in the display section, it is necessary to adopt a technique to make the device to be mounted invisible to human eyes so as not to block a user's sight.
A technique of using a transparent conductive film to form such a device in a microwave band or a millimeter band or transmission lines to that device is known, for example. Patent Document 1, for example, discloses a transparent electrode having excellent etching property and high transmittance.